Question

Is $ {{C}_{2}}^{-} $ paramagnetic or diamagnetic?

Answer 1

Hint: To determine whether a molecule is paramagnetic or diamagnetic, one must first determine the molecule's molecular electronic configuration. When a molecule contains unpaired electrons, it is called paramagnetic, and when it has paired electrons, it is called diamagnetic.

Complete answer:
A magnetic field repels diamagnetic materials because it induces an induced magnetic field in them in the opposite direction, resulting in a repulsive force. Magnetic fields, on the other hand, attract paramagnetic and ferromagnetic materials. Diamagnetism is a quantum mechanical phenomenon that occurs in all materials and is referred to as diamagnetic when it is the only contribution to magnetism.
Some materials are weakly attracted by an externally applied magnetic field and produce internal, induced magnetic fields in the direction of the applied magnetic field, which is known as paramagnetism. Diamagnetic materials, on the other hand, are repelled by magnetic fields and produce induced magnetic fields in the opposite direction of the applied magnetic field. The majority of chemical elements and some compounds are paramagnetic.
Carbon possesses one 1s, one 2s, and three 2p orbitals (the 1s orbital is significantly less energetic than the 2s and 2p orbitals). We don't need to worry about the 1s electrons; their energy is so low that they may be removed from the MO diagram.
Each carbon atom contains four valence electrons, two of which share the same 2s orbital and two of which occupy two of the three 2p orbitals individually.
Two carbons linked together must have a total of eight valence electrons since one carbon has four. This yields the number of valence electrons in $ {{C}_{2}} $ , but not the number of valence electrons in $ {{C}_{2}}^{-} $ .
It corresponds to 10.
Hence using molecular orbital diagram
 $ {{\left( {{\sigma }_{1s}} \right)}^{2}}{{\left( \sigma _{1s}^{*} \right)}^{2}}\overbrace{{{\left( {{\sigma }_{2s}} \right)}^{2}}{{\left( \sigma _{2s}^{*} \right)}^{2}}{{\left( {{\pi }_{2{{p}_{x}}}} \right)}^{2}}{{\left( {{\pi }_{2{{p}_{y}}}} \right)}^{2}}}^{\text{valence electrons }}{{\left( {{\sigma }_{2{{p}_{z}}}} \right)}^{2}} $
There are no unpaired electrons, hence it is diamagnetic in nature.

Note:
Diamagnetism is a characteristic of all materials that contributes just a little amount to their reaction to a magnetic field. Other types of magnetism (such as ferromagnetism or paramagnetism) are so much stronger that the diamagnetic contribution is generally insignificant when many forms of magnetism are present in a material. Diamagnetic materials, or diamagnets, are substances that exhibit the strongest diamagnetic behaviour.